Copolymers of ethylene and their use in the preparation of foamable plastics

Abstract

A foamable copolymer comprising 40 to 98 percent by weight units of ethylene, 1 to 30 weight percent units of vinyl alcohol, 1 to 30 weight percent units of acrylic acid ester of a secondary or tertiary alcohol, and up to 2 percent by weight of vinyl acetate units is described together with a process for the manufacture thereof. The same is useful in the formation of a foamed mass which is relatively highly cross-linked. The copolymer can be foamed to form a foam by heating the same at 250° to 350° C. for 5 to 60 minutes in the absence of oxygen.

What is claimed is: 
     
       1. A foamable copolymer comprising 40 to 98 percent by weight of ethylene units, 1 to 30 percent by weight of vinyl alcohol units, 1 to 30 percent by weight of acrylic acid ester units of secondary or tertiary alcohols and up to 2 percent by weight of vinyl acetate units. 
     
     
       2. A foamable copolymer according to claim 1, wherein the acrylic acid ester units are units of a tertiary alcohol having 4 to 8 carbon atoms. 
     
     
       3. A process for foaming a copolymer according to claim 1 which comprises heating said copolymer for 5 to 60 minutes at 250° to 350° C. in the absence of oxygen. 
     
     
       4. A process for preparing a copolymer according to claim 1 which comprises saponifying a copolymer having 40 to 98 weight percent units of ethylene, 1.5 to 50 weight percent units of a vinyl ester and 0.5 to 10 weight percent units of an acrylic acid ester with an alcoholic solution of an alkali metal hydroxide. 
     
     
       5. A foamed cross-linked copolymer of a saponified copolymer of ethylene, vinyl alcohol and an acrylic acid ester of a secondary or tertiary alcohol which saponified copolymer contains vinyl acetate in an amount of up to 2 percent by weight based upon the combined amount of the weight of the units of ethylene, vinyl alcohol and acrylic acid ester, said saponified copolymer comprising 40 to 90 percent by weight ethylene units, 1 to 30 percent by weight vinyl alcohol units and 1 to 30 percent by weight acrylic acid ester units. 
     
     
       6. A foamed cross-linked copolymer according to claim 5 wherein said acrylic acid ester units are ester units of a tertiary alcohol having 4 to 8 carbon atoms. 
     
     
       7. A foamed cross-linked copolymer according to claim 5 wherein said acrylic acid ester units are acrylic acid ester units of an alcohol selected from the group consisting of secondary butanol, tertiary butanol, secondary pentanol and tertiary pentanol. 
     
     
       8. A polymer according to claim 5 wherein said polymer prior to saponification comprises 15 to 96.8 percent by weight ethylene units, 1.2 to 45 percent by weight of vinyl ester units and 2 to 40 percent by weight of acrylic acid ester units derived from secondary or tertiary alcohols. 
     
     
       9. A process for preparing a copolymer according to claim 5 which comprises: (A) forming a terpolymer of ethylene, vinyl acetate and an acrylic acid ester of a secondary or tertiary alcohol so that such polymer comprises 15 to 96.8 percent by weight ethylene units, 1.2 to 45 percent by weight vinyl acetate units and 2 to 40 percent by weight of acrylic acid ester units;   (B) saponifying the polymer of step A so that it still contains vinyl acetate units, the vinyl acetate units being present in the polymer in an amount of up to 2 percent by weight; and   (C) subjecting said saponified copolymer to sufficient heat to effect thermal cleavage of said acrylic acid ester and olefin whereby said saponified copolymer is foamed and cross-linked.   
     
     
       10. A process according to claim 9 wherein: (1) the polymer of step A is formed by forming a polymerization reaction mixture comprising 40 to 98 percent by weight of ethylene, 1.5 to 50 percent by weight of a vinyl ester and 0.5 to 10 percent by weight of an acrylic acid ester of a secondary or tertiary alcohol and said polymerization reaction mixture is subjected to a pressure of 400 to 4,000 bars at a temperature of 110° to 350° C. for sufficient time to form a polymer comprising 15 to 96.8 percent by weight ethylene, 1.2 to 48 percent by weight of vinyl acetate units and 2 to 40 percent by weight of acrylic acid ester units:   (2) the polymer obtained from step 1 is saponified by contacting the same with an alcoholic solution of an alkali metal hydroxide, the alcohol being a C 1  to C 4  alcohol and the alkali metal hydroxide being present in an amount of 1 to 10 weight percent at a temperature of 60° to 120° C. for 120 to 180 minutes; and   (3) the product obtained from step 2 is heated for 5 to 60 minutes at a temperature of 250° to 350° C. sufficient to effect thermal cleavage of the acrylic acid ester and formation of a cross-linked foamed copolymer.